Automatic Shut-Off Valve For The Oil Circuit In An Airplane Engine

ABSTRACT

The present invention concerns a lubrication system in a closed circuit provided with a valve comprising a first position and a second position, as well as an IN inlet, a first BP outlet and a second M outlet, said IN inlet being connected to the outlet of the feed pump, the first BP outlet being connected to the bypass circuit and the second M outlet being connected to the feed circuit. In the first position of the valve, the flow entering via the IN inlet is diverted to the first BP outlet and in the second position, the incoming flow is diverted to the second M outlet, said valve switching from the first position to the second position and vice versa, when the incoming flow rate exceeds a predetermined threshold upwards and downwards respectively.

SUBJECT OF THE INVENTION

The present invention concerns an automatic shut-off and isolation valvefor the oil circuit in an aircraft engine, in particular in a turbojetor a turboprop.

STATE OF THE ART

With certain turbojets, when the aircraft is stopping, it is interestingto stop or reduce the oil supply to the bearing housings before theaircraft has completely stopped, so as to permit a complete drainage ofthese housings, whilst the rotation is ceasing. In fact, in theseaircraft, the oil is supplied to the housings by a pump, the feed pump,and collected at the bottom of these housings by another pump, thecollection pump. Both pumps being of a volumetric type and driven by themain shaft of the engine or HP shaft, they continue to work until thisshaft comes to a complete stop.

In certain cases, an imbalance may occur between the oil supplied by thefeed pump and the collection pump or pumps, which may cause an excess ofoil to appear in the housing and cause leaks

This imbalance may also lead to the stagnation of oil in the housingsduring stopping phases of the engine and may cause the coking of thestagnant oil, especially in engines with one or several housings whichare particularly hot or particularly sensitive to the phenomenon knownas “soak back”, of the temporary heating of the mechanical parts whenthe engine is stopped.

Document U.S. Pat. No. 4,170,873 describes a system comprising 2 valves,one for safety and the other for control, allowing to control the oilflow fed to the bearing housings during running phases at low speed.These valves are controlled by the pressure in the various circuits.

Document U.S. Pat. No. 4,245,465 describes a 3-function valve allowingfor one thing to reduce the oil flow fed to the bearing housings duringrunning phases at low speed, to cut the supply of oil to the housings atvery low speed and to control the oil flow at high running speed. Thisvalve continuously lets oil flow to the oil tank; it therefore neverlets the full flow be fed to the engine.

The so-called “anti-siphon” devices provided for blocking any leak fromthe tank through the pump to the bottom areas of the engine duringperiods of inactivity occurring during the last turns of the engine mayplay a part in reducing the quantity of stagnant oil. They act byshutting off either the connection from the oil tank to the feed pump orthe outlet of the pump under a certain pressure.

Whatever the “anti-siphon” methods used, they have the commoncharacteristic of acting very late during the stopping phase, even afterthe engine has completely stopped and if this is not the case, ofsometimes significantly slowing down the ignition on restart. Theresumption of the oil supply during restart thus occurs systematicallyat a significantly higher speed than that at which the flow was cut offduring stopping. Moreover the control of such devices to get a cut-offat a significant speed during stopping, so as to ensure a good drainage,might lead to make the re-ignition of the pump impossible on restart.Certain “anti-siphon” devices do not show this disadvantage, but thenthey are based on a more or less complex control system, which oftenconsumes oil, and which is useless in many engines.

None of these systems allows to efficiently prevent the stagnation ofoil in the housings during the stopping phases of the engine. Inparticular, none of these systems describes a device that would preventthe phenomenon of coking of the stagnant oil.

AIMS OF THE INVENTION

The present invention aims to provide a solution to the disadvantages ofthe state of the art.

In particular, the invention aims to provide a simpler and lighter meansthan the devices known in the state of the art (“anti-siphon” devices,U.S. Pat. No. 4,245,465, U.S. Pat. No. 4,170,873, etc.), which can actat any moment during the stopping phase of the engine and which allowson restart to resume the supply at a speed equal or very close to thatat which the flow was cut off during stopping.

Moreover, the present invention aims to achieve this objective with asimple and compact valve without complicated control and scarcelysensitive to friction and pollution.

MAIN CHARACTERISTIC FEATURES OF THE INVENTION

A first aspect of the present invention concerns a lubrication system ina closed circuit comprising:

-   -   a feed pump;    -   an oil tank;    -   a feed circuit supplying the oil to housings (20) containing        parts to be lubricated;    -   a collection circuit returning the oil from the housings to the        tank;    -   a bypass circuit returning the oil from the outlet of the feed        pump to the tank or to the inlet of the feed pump;    -   a valve comprising a first position and a second position as        well as an IN inlet, a first BP outlet and a second M outlet,        said IN inlet being connected to the outlet from the feed pump,        the first BP outlet being connected to the bypass circuit and        the second M outlet being connected to the feed circuit;        characterized in that, in the first position, the flow entering        via the IN inlet is diverted to the first BP outlet and, in the        second position, the incoming flow is diverted to the second M        outlet, said valve switching from the first position to the        second position and vice versa, when the incoming flow exceeds a        predetermined threshold upwards and downwards respectively.

According to preferred embodiments of the invention, the lubricationsystem comprises at least one or any suitable combination of thefollowing characteristics:

-   -   said valve comprises a valve which slides slightly loose in a        bore machined into a valve body between two opposite seats, a        first seat being connected to the IN inlet and a second seat        being connected to the BP outlet, the M outlet emerging in the        bore in a ring-shaped cavity surrounding the first seat, so        that:        -   for a flow rate in the IN inlet lower than the predetermined            threshold, the valve is pushed by a spring (5) on the first            seat controlling the IN inlet (1) and the connection from            the IN inlet (1) to the ring-shaped cavity (8) is blocked,            the connection being opened towards the BP outlet via at            least one calibrated opening passing through the valve and            emerging laterally in the bore upstream from the seat of the            BP outlet;        -   for a flow rate from the IN inlet greater than or equal to            the predetermined threshold, the valve moves to the second            seat in a position where it rests against the second seat,            closing the BP outlet and where the IN inlet is connected to            the M outlet via the ring-shaped cavity, the first seat            being released by the movement of the valve    -   the valve is made of at least two parts which push against each        other.    -   the seal of any outlet or of the two outlets of the valve is        provided by means of a cover principle of the “sliding type”        replacing the seat-valve contact.    -   said valve comprises a valve which slides in a bore between two        opposite seats, a first seat being connected to the M outlet and        a second seat being connected to the BP outlet the IN inlet (1)        emerging in the bore in a ring-shaped cavity surrounding the        first seat and the bore or the valve comprising at least one        calibrated channel between the two seats the parts of said valve        being proportioned in such a way that:        -   for a flow rate from the IN inlet (1) lower than the            predetermined threshold, a spring (5) holds said valve (4)            rested against the first seat (23), closing the M outlet            (2), the flow being diverted towards the BP outlet (3);        -   for a flow rate from the IN inlet (1) greater than or equal            to the predetermined threshold, said valve (4) moves to the            second seat (24), opening the M outlet (2) and closing the            BP outlet    -   the valve (4) is spherical.

A second aspect of the invention concerns an aircraft engine comprisinga lubrication system such as described above. This engine is for examplea turbojet, a turboprop, a turboshaft or a helicopter engine.

As an advantage, in such an engine, the lubrication system and saidvalve are located in one casing.

BRIEF DESCRIPTION OF THE DIAGRAMS

Diagrams 1A and 1B show a valve according to a first particularembodiment of the invention.

Diagrams 2A and 2B show a valve according to a second particularembodiment of the invention.

Diagrams 3A and 3B show a valve according to a third particularembodiment of the invention.

Diagrams 4A and 4B show a valve according to a fourth particularembodiment of the invention.

Diagrams 5A and 5B show a valve according to a fifth particularembodiment of the invention.

Diagram 6 shows schematically a lubrication system according to thepresent invention.

Diagram 7 shows a scheme of the principle of an aircraft engine equippedwith an automatic shut-off valve for the oil circuit according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, the flow from the feed pump to theengine is cut off before the engine has completely stopped, whilstletting the collection pumps operate normally. From this moment onwards,the collection pumps will drain the housings efficiently, since theycontinue to suck in the oil flowing from the wet components and walls,without any new oil being fed in.

In the event of such an interruption in the flow supply during stopping,it is nevertheless necessary to ensure that the engine is resuppliedearly enough on restart.

This cutting off of the oil flow supply when the engine is stopped thuspermits to combat the coking in aircraft engines.

In the present invention, this function of stopping the flow supply tothe housings is achieved by means of a shut-off and “bypass” valve. Thisvalve comprises three ways and two positions. It is placed at the outletof the feed pump (IN way) and diverts the flow from the pump to the tankor the inlet of the pump (BP way, stands for “bypass”) when this flow isweak, whilst closing the connection to the engine (M way). When the flowfrom the pump reaches a predetermined threshold, it diverts this flow tothe engine (M way) and closes the connection to the tank or the inlet ofthe pump (BP way) again.

Particular embodiments of the valve according to the invention are shownin Diagrams 1A, 1B, 2A, 2B, 3A, 3B, 4A, 4B, 5A and 5B.

In a first particular embodiment of the invention shown in Diagrams 1Aand 1B, the valve is composed of a valve 4, which slides slightly loosein a bore 7, between two opposite seats 10, 11. One is connected to theIN way, the other to the BP way. The M way emerges in a ring-shapedcavity 8 surrounding the IN seat.

At rest or whilst the flow via the IN way is lower than a predeterminedthreshold, the valve 4 is pushed by a spring 5 towards the seat 10controlling the IN way and the connection from the IN inlet to thering-shaped outlet 8 emerging in the M way is blocked (Diagram 1A).However, the connection is possible to the BP, via the calibratedopening 9 emerging in the cavity 12 defined by the bore 7 upstream fromthe seat 11 of the BP way.

The pressure of the IN way thus applies to the surface of the valveresting on the seat 10. Since the BP way is connected to the tank 16 orthe inlet of the pump, it is considered to be at zero pressure and thepressure of the IN way is controlled by the flow of the IN way,controlled by the volumetric feed pump 17 (Diagrams 6 and 7) and passingthrough the connection channel 9, whose hydraulic resistance iscalibrated. When the force exerted by this pressure on the valve 4 isless than the load of the spring 5, the valve presses against the seat10 of the IN way and closes the M way (Diagram 1A).

When, as a result of an increase in the flow from the pump, thispressure becomes greater than the load of the spring 5 in this position,the valve moves to the other seat, creating additional hydraulicresistance to the flow and increasing the pressure differential appliedto the valve 4. This functioning is verified provided that the M wayoffers significant hydraulic resistance (which is generally the casewith aircraft engines) and that the way from the connecting channel 9between the two seats 10, 11 is properly suited to it.

At higher flow rates, the valve 4 comes to rest against the seat 11emerging in the BP way, which is thus completely closed, and thepressure of the engine circuit applies to the entire surface of thevalve 4 on the side of the M way, which is locked in this position bythe pressure (Diagram 1B). When the flow rate drops, the resultingdecreasing in pressure allows the spring to push the valve back to itsoriginal position (Diagram 1A).

The fluctuation levels in one direction and the other, the functionalhysteresis and the stability are controlled by the ratios of the surfaceareas of the seats, the preload, the direction and stiffness of thespring 5 and the ratio of the hydraulic resistance of the connectingchannel 9 relative to that of the M way.

In other particular embodiments of the invention:

-   -   the valve may be of any shape, provided that the hydraulic        principles mentioned above are observed;    -   the valve might be made in two or more parts that are more or        less fixed and which push against each other;    -   the connecting channel may be made in various ways (see an        alternative in Diagrams 2A and 2B).

The seal of any outlet or of the two outlets of the valve according tothe invention could also be realized by means of the cover principle ofthe “sliding type” 13, instead of a seat-valve-valve piece contact. Thisprinciple is illustrated in Diagrams 3A and 3B.

In another alternative embodiment shown in Diagrams 4A, 4B, 5A and 5B,the valve is composed of a valve 4, which slides in a bore 7 between twoseats 23, 24. Depending on its position and the seat which it is restingon, it opens or closes the connection to the BP or M ways. At rest(Diagrams 4A and 5A), the valve 4 is pushed by a spring 5 to the seat 23controlling the M way, which it closes. The valve 4 or the bore 7 isalso fitted with one or more calibrated connections 15 allowing theconnection between the ring-shaped zones located around the seats 23, 24on both sides of the valve 4. The IN way emerges via the bore 7, in thering-shaped space surrounding the seat 23 of the M way. The pressure ofthe IN way thus applies to the ring-shaped surface of the valve aroundthe seat 23. Since this zone is connected to the BP way, which is openby means of the calibrated channel 15, the flow moves from the IN way tothe BP way, the M way being closed by the spring 5. Since the BP way isconnected to the tank 16 or the inlet of the pump 17 (Diagrams 6 and 7),it is considered to be at zero pressure and the pressure of thering-shaped zone of the valve 4 around the seat 23 of the M way iscontrolled by the flow passing through the connecting channel 15. Whenthe force exerted by this pressure on the valve 4 is lower than the loadof the spring 5, the valve 4 remains rested against the seat 23 of the Mway and keeps it closed (Diagram 4A). When, as a result of an increasein the flow from the pump 17, this pressure becomes greater than theload of the spring 5 in this position, the valve moves to the other seat24, creating additional hydraulic resistance to the flow and increasingthe pressure differential applied to the valve 4. At the same time, theflow begins to move towards the M way and the IN pressure spreadsprogressively to a greater surface area of the valve, increasing theimbalance. This functioning is verified, provided that the M way offerssignificant hydraulic resistance (which is generally the case withengines) and that the way of the connecting channel 15 between the twoseats 23, 24 is properly suited to it. At higher flow rates, the valve 4is rested against the seat 24 of the BP way, which is completely closed,and the pressure of the engine circuit applies to the entire surface ofthe valve on the M side, which is locked in this position by thepressure (Diagram 4B). When the pressure drops, the decreasing inpressure allows the spring 5 to push the valve 4 back to its originalposition (Diagram 4A). The fluctuation levels in one direction and theother, the functional hysteresis and the stability are controlled by theratios of the surface of the seats, the preload, the direction andstiffness of the spring 5 and the ratio of the hydraulic resistance ofthe connecting channel 15 relative to that of the M way.

In one embodiment of the invention, the valve 4 is of a spherical shapeas shown in Diagrams 4A and 4B.

In particular embodiments of the present invention, the calibratedconnection between the two sides may advantageously be realised in thevalve itself as shown in Diagrams 5A and 5B, by grooves in the bore oreven via an external channel.

1. A lubrication system in a closed circuit comprising: a feed pump(17); an oil tank (16); a feed circuit (19) supplying the oil tohousings (20) containing parts to be lubricated; a collection circuit(21) returning the oil from the housings (20) to the tank (16); a bypasscircuit (18) returning the oil from the outlet of the feed pump (17) tothe tank (16) or to the inlet of the feed pump (17); a valve (22)comprising a first position and a second position as well as an IN inlet(1), a first BP outlet (3) and a second M outlet (2), said IN inlet (1)being connected to the outlet from the feed pump (17), the first BPoutlet (3) being connected to the bypass circuit (18) and the second Moutlet (2) being connected to the feed circuit (19); characterized inthat, in the first position, the flow entering via the IN inlet (1) isdiverted to the first BP outlet (3) and, in the second position, theincoming flow is diverted to the second M outlet (2), said valveswitching from the first position to the second position and vice versa,when the incoming flow exceeds a predetermined threshold upwards anddownwards respectively.
 2. Lubrication system as in claim 1,characterized in that said valve (22) comprises a valve (4) which slidesslightly loose in a bore (7) machined into a valve body (6) between twoopposite seats (10, 11), a first seat (10) being connected to the INinlet (1) and a second seat (11) being connected to the BP outlet (3),the M outlet (2) emerging in the bore (7) in a ring-shaped cavity (8)surrounding the first seat (10), so that: a. for a flow rate in the INinlet (1) lower than the predetermined threshold, the valve (4) ispushed by a spring (5) on the first seat (10) controlling the IN inlet(1) and the connection from the IN inlet (1) to the ring-shaped cavity(8) is blocked, the connection being opened towards the BP outlet (3)via at least one calibrated opening (9) passing through the valve (4)and emerging laterally in the bore (7) upstream from the seat (11) ofthe BP outlet (3); b. for a flow rate from the IN inlet (1) greater thanor equal to the predetermined threshold, the valve (4) moves to thesecond seat (11) in a position where it rests against the second seat(11), closing the BP outlet (3) and where the IN inlet (1) is connectedto the M outlet (2) via the ring-shaped cavity (8), the first seat (10)being released by the movement of the valve (4).
 3. Lubrication systemas in claim 2, characterized in that the valve (4) is made of at leasttwo parts which push against each other.
 4. Lubrication system as inclaim 2, characterized in that the seal of any outlet or of the twooutlets of the valve (22) is provided by means of a cover principle ofthe “sliding type” (13) replacing the seat-valve contact.
 5. Lubricationsystem as in claim 1, characterized in that said valve (22) comprises avalve (4) which slides in a bore (7) between two opposite seats (23,24), a first seat (23) being connected to the M outlet (2) and a secondseat (24) being connected to the BP outlet (3), the IN inlet (1)emerging in the bore (7) in a ring-shaped cavity surrounding the firstseat (23) and the bore (7) or the valve (4) comprising at least onecalibrated channel (15) between the two seats (23, 24), the parts ofsaid valve (22) being proportioned in such a way that: c. for a flowrate from the IN inlet (1) lower than the predetermined threshold, aspring (5) holds said valve (4) rested against the first seat (23),closing the M outlet (2), the flow being diverted towards the BP outlet(3); d. for a flow rate from the IN inlet (1) greater than or equal tothe predetermined threshold, said valve (4) moves to the second seat(24), opening the M outlet (2) and closing the BP outlet (3). 6.Lubrication system as in claim 5, characterized in that the valve (4) isspherical.
 7. Aircraft engine comprising a lubrication system as inclaim
 1. 8. Aircraft engine as in claim 7, characterized in that it is aturbojet, a turboprop, a turboshaft or a helicopter engine.
 9. Aircraftengine as in claim 7, characterized in that said lubrication system andsaid valve (22) are located in one casing.